1. Field of the Invention
The present invention relates to an optical pickup device for reproducing and recording information from and to an optical disc such as a CD (compact disc) or DVD (digital versatile disc) used as an information recording medium.
2. Description of Related Art
An optical pickup device is provided with an optical head that shines laser light on a recording surface of a rotating optical disc to write information to the recording surface (thus to perform recording) and that receives the laser light reflected from the recording surface of the optical disc to read information from the recording surface (thus to perform reproduction). Here, during the reproduction and recording of information from and to the optical disc, the optical head moves so as to reciprocate across the recording surface of the optical disc in the direction of a radius thereof. This reciprocating movement is generally guided by a pair of guide rods supported on a chassis. Thus, whether reproduction and recording can be performed with high accuracy depends greatly on how parallel the guide rods are to the recording surface of the optical disc. For this reason, in a common optical pickup device, to permit adjustment of the parallelism just mentioned, the guide rods are supported on the chassis in such a way that their height can be adjusted.
An example of a conventional structure that permits adjustment of the height of the guide rods is shown in FIG. 4. It should be noted that, although in reality each guide rod has two ends (both ends) and thus a pair of guide rods has four ends in total, FIG. 4 shows a part around only one of them, as a representative of all the four.
As shown in FIG. 4, on a chassis (unillustrated), near an end 102a of a guide rod 102, a twist coil spring 104 is fitted. Through a coil portion 104a of this twist coil spring 104, the guide rod 102 is placed. Both end portions 104b of the twist coil spring 104 that extend outward therefrom are hooked on the chassis, and thereby the twist coil spring 104 is fitted to the chassis. In this way, the resilient restoring force of the twist coil spring 104 is applied to the guide rod 102, and thus the guide rod 102 is kept loaded with a force that tends to move the guide rod 102 away (downward in FIG. 4) from the recording surface of the optical disc (located above in FIG. 4) as indicated by a solid-line arrow in FIG. 4.
Also on the chassis, near the end 102a of the guide rod 102, a special screw 105 is fitted. By being rotated, this special screw 105 moves closer to and away from the recording surface of the optical disc. This special screw 105 has a flat end face 105aa, with which the part of the outer circumferential face of the guide rod 102 near the end 102a thereof makes contact. This restricts the movement of the guide rod 102 in the direction in which it is loaded with the force, and thereby determines the position, and hence the height, of the part of the guide rod 102 near the end 102a thereof. The special screw 105 is fitted to the chassis by being screw-engaged into a threaded hole that is formed by tapping or otherwise processing the chassis, which is molded of synthetic resin such as polyphenylene ether (PPE). By a bracket formed on the chassis, the guide rod 102 is guided to be movable in the direction in which it is loaded with the force, and is prevented from moving in other directions (such as the direction perpendicular to the plane of the figure in FIG. 4).
Likewise, near each of the other three ends 102a of the guide rods 102, a twist coil spring 104 and a special screw 105 are fitted.
In the construction described above, by rotating the special screws 105 individually to screw them in and out and thereby move them forward and backward, it is possible to adjust the height of the guide rod 102 near each end 102a thereof. This permits the guide rods 102 to be adjusted to be properly parallel to the recording surface of the optical disc.
In another example of a conventional structure that permits adjustment of the height of the guide rods, a pair of plate springs is provided to load with a force the part of the guide rods close to each end 102a thereof, and a special screw is provided that, by being rotated, moves closer to and away from the recording surface of the optical disc (this screw moves forward and backward in the same direction as the special screw 105 described above) (see, for example, JP-A-2003-346351). Here, the special screw has a head portion with a wide extending circumferential rim. With the outer end face of the circumferential rim, the part of the outer circumferential face of a guide rod 102 near an end 102a thereof makes contact. This permits the height of the guide rod 102 near each end 102a thereof to be determined.
On the other hand, in recent years, optical pickup devices have been required to be increasingly inexpensive. Disadvantageously, however, the conventional guide rod height adjustment constructions described above both require special screws that are fabricated for dedicated purposes and that are thus difficult to obtain in the ordinary market. This greatly limits the possibility of cost reduction for the following reasons. In the special screw 105 used in the first example of the conventional guide rod height adjustment constructions described above, the end face 105aa, which makes contact with a guide rod 102, is required to offer a high degree of perpendicularity relative to the rotation center axis (this is not much the case with screws fabricated for general purposes). On the other hand, in the special screw used in the second example, to permit it to make contact with a guide rod 102, at the head portion of the screw, a wide extending circumferential rim needs to be formed (which is unlikely to be found in screws fabricated for general purposes).
Incidentally, in the second example of the conventional guide rod height adjustment constructions described above, the guide rod 102 is held in position by plate springs and special screws. Thus, the outer circumferential face of a guide rod 102 may accidentally slip off the outer end face of the head portion of the special screw, causing the guide rod 102 to drop off.